Stabilized radioreceiver



July 25, 1933. w. VAN B. ROBERTS STAB ILI ZED RADIORECEIVER Filed April 15 INVENTOR WALTER VAN B- ROBERTS BY 7 ATTORNEY patented July 25, 1933 I t UNITED STATES PAT WALTER v B.

E-NT OFFICE I ROB RTS, or rnmon ron, nnw mnsnr, AssIenon 'roRAnIo OORPORA TION on MERICA; A CORPORATION OF DELAWARE STABILIZED n Anroitncnrvnn Application filed April 15, 1929.0 S eriaI No. 355,006.

a t The present invention relates to stabilized radio receivers, and,more particularly, to a receiver which islstable at all frequencies,

and, additionally, has itsfidelity unimpaired at the-low frequency end.-

The distinguishing feature of the present invention involvesla radioreceiver which is stabilized at long Wave lengths by means of capacitive reactance in the late circuit, and at short wave lengths, chie y by means of a counter feed back arrangement. The impors tant advantage of this arrangement that the tuning of the receivingsystem at the long ,wave lengths can be rendered abnormally broad by. the use of a sufiicient amount of capacitiverea'ctance in the plate circuit. The importance of this advantage will be readily observed, when it is realized that the ordinary neutralized receivers possess too sharp a tuning characteristicat the long wave lengths for good fidelity.

At the shortwave end, however, there is no necessityfor anyextrabroadening oft he tuning, and this fact fits in well with the fact that the reactance of aifixed condenser in the plate circuit becomessosmall at high frequencies that it does not cause broadening of the tuning. Notonly that; indeed, it befrequency increases.

duce aycounter feed back in comes so small that it is likely to beinsufli-v cientto. prevent actual oscillations from occurring. Therefore, for this reason, I introproportion as the Such counter feed back maybe introduced in any desired fashion. Forexample, a mag netic counter feed iback'ispossible, the feed back control being adjusted either fixedly, or it may be varied bythetuning condenser wherestability is not Obtained by reactance inthe plate circuit. Again, feed back-may be arranged to the grid circuit by means of a condenser (connectedto theplate circuit) which controls the amount of current "allowed to flow in a coil which is either coupled to the grid circuit or a part thereof. 3

The capacity of this feed back condenser is adjusted to insure stability at the short a wave lengths, and may if desired, be varied according to: frequency, However, such vacasethe feed back coil comes nearerto resonating with the feed back condenser at high frequencies than at low, resulting in less than neutrahzationtat long wave lengths, if

tion at short-waves. v v v The above discussion presents the various adjustment is made for complete neutralizapossibilities involved in the problem of stay bilizing a tuned radio frequency radio re-' ceiver at all frequencies, emphasis being placed on theunimpairment of fidelity at the 'low frequencyend. However, I have devised a radio receiver wherein there is a transition from stabilization from long wave lengths, by means of capacitive reactance in the plate circuit, to stabilization at short wave lengths chiefly by means of counter feed back, in a very novel and practical manner. In the actual construction of the receiver which I have reduced to practice, there is embodied a means forobtaining neutralization at short waves, with lessthan full neutralization at long waves. :Briefly, by using areverse connection between. the primary and secondary coils of the radio frequency transformers, and by using a type of gang condenser for tuning whichhas its rotor grounded, there is obtained neutralization at short waves through the capacity between the stators ofthe gang condenser.-- As the Wave length is increased, however, this capacity between the stators is wiped out by the end plates of the rotors which enclosethe stators'likeashield. c i

Accordingly, it is one of the many'objects of the presentinvention to provide av radio receiver which is stable at all frequencies,

has its fidelity unimpaired atthe low frequency ,end, and comprises a tuned radio frequency receiving circuit which includes a seriescondenser inueach Of the plate circuits withvariable feedback which approaches complete neutralization at the shortwave end. A t Another important object of the invention is to providea tuned radio receiver, which is stable at all frequencies, including reverse connections between the primary and secondary coils of the radio frequency transformers and a tuning condenser so constructed and arranged in the receiving circuit that neutralization at short waves is obtained through the capacity between the stators of the condensers, this capacity between stators being wiped out by the end plates of the rotors as the wave length is increased.

Other objects of the invention are to improve chiefiy the simplicity and efficiency of such devices and to provide a radio receiver of the tuned radio frequency type which is economical to manufacture and stable in operation.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

The drawing shows a grounded antenna circuit A,G connected to the input in the first stage of a tuned radio frequency amplifier which includes a triode 1, having its filament grounded for alternating currents. The coupling between the antenna circuit and the tuned input circuit of triode 1 may be varied at coil L as shown in the drawing. The input circuit of triode 1 is tuned by a variable condenser C S this condenser being one of a gang of condensers mounted in the well known manner upon a single shaft whereby uni-control may be obtained.

Triode 2 designates a second stage of tuned radio frequency amplification, while triode 3 is a detector tube. Each of the input circuits of these three tubes is tuned by a variable condenser, as is explained before, all of these condensers being mounted on a single shaft, in a uni-control manner. The rotors C C C are revolved simultaneously while the capacity between the stators S S S of the gang condenser is utilized to obtain neutralization at short waves. I

The plate circuits of triodes 1 and 2 are energized through choke coils I, I from a source, preferably, of 135 volts, it being understood that these choke coils'have nothing to do with the radio frequency operation. For optimum operation a condenser C. of a magnitude of about'.0O025 microfarads is inserted in the plate circuit of tube 1 between the choke coil I, and the primary coil L of the radio transformer, it being observed that a condenser C of a magnitude of about .0003 microfarads is similarly. disposed in the plate circuit of triode 2. These values were determined experimentally.

Resistances R R are inserted in. the cathode leads of t-riodes 1 and 2 for the purpose of obtaining bias. They have nothing to do with the radio frequency operation, it being noted that each of the resistances is shunted-by condenser c or 0 A reverse connection is employed between the primary and secondary coils of the radio frequency transformer M and M the turn ratio between coils L and L being about 1:4, and the ratio between primary coil L and secondary coil L5 of the radio transformer M also being approximately 1: 4.

The grid condenser C is shunted by a grid resistance Gr inserted in the grid circuit of detector triode 3, the plate circuit of detector triode 3, being energized by a source B. A condenser C of a magnitude of about .0005 microfarads is connected between plate and cathode, the output from the detectorbeing connected to any utilization means such as phones, loud speaker, etc.

The operation of the circuit disclosed has been found very satisfactory, and results in stabilization at all frequencies, unimpaired fidelity being secured, in particular, at the lowfrequency end. It will be observed that neutralization is obtained at short waves through the capacity between the stators S S and of the gang condenser,

V it'being noted that the rotors C C (1 of the said gang condenser are all grounded and uni-controlled.

As the wave length is increased, this capacity between the stators is wiped out by the end plates of the rotors which enclose the stators like a shield. This type of condenser is well known, and it is believed that the diagrammatic showing thereof will readily teach those skilled in the art the manner of employing the same in the circuit of the type disclosed. It will be noted that the series condenser C C in the plate circuits of each of the tubes 1, 2 combine with the variable feed back to produce approximately complete neutralization at the short wave end, it being especially observed that less than full neutralization is employed at long waves. It will thus be obvious that the distinguishing feature of the present receiver is the transition from stabilization at long wave lengths chiefly by means of capacity reactance in the plate circuit to neutralization at short waves chiefly by means of counter feed back.

While I have indicated and described one system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many more modifications in the circuit arrangement may be used, 'as well as in the apparatus employed,

ago

without departing from the scope. of my in vention as set forth in the What I claim is: 1. A radio receiver comprising signal energy collecting 'means, a plurality of tuned radio frequency amplification stages, eachof saidstages including anelectron disappended claims.

charge device, .a seriescondenser in the anode circuit of each of said devices, a unicontrolled tuning capacity common to the input circuits of each of said stages, and means including the capacitance between stators of said tuning capacity for produc-. ing variable feed back which approaches complete neutralization at the short wave end. l

2. A radio receiver including a plurality of tuned radio frequency amplifier stages, each of said stages including a fixed condenser in its plate circuit, a uni-control eondenser common to the input circuits of said stages, means including the capacitance between the stators of the uni-control condenser for. introducing a counter feed back in proportion as the frequency increases,"for

obtaining neutralization at short waves.

3. A radio receiver which is stabilized at all'frequencies and has its fidelity unimpaired at its low frequency end comprising,

a signal energy collecting means, a plurality of amplifying stages coupled thereto, each of said stages including a triode having a fixed capacitance in its plate circuit, the

coupling between stages comprising a reverse coupling between the primary and secondary coils of. the radio frequency transformers, a uni-control condenserhaving the rotors thereof grounded, and common to the input circuits of said stages, the circuit being so arranged that neutralization at shortwave lengths is obtained through the capacity between the stators of the uni-control condenser. i a

4. In combination,aplurality of resonant high frequency circuits, "an electron discharge repeater for coupling each succeeding pair of circuits, a common variable capacitance for tuning all of said circuits through aran e of frequencies, means for counteracting eed back of energy through said repeaters, and additional means, in-

of said range,

cluding capacitive reactance produced durmg a portion of the variation of said common capacitance, for aiding said counteracting means duringtuning to the higher portion of said range.

5. A radio receiver comprising a plurality of tuned amplifier stages, each stage including a repeater, the output circuit of" each repeater being coupled to the input circuit of a succeeding repeater by an inductive coupling having a turn ratio, be-

tween primary and secondary, of about 1: 4,

a uni-controlled gang of variable condensers said repeaters, and additional means, including the capacity between at least one stator in each condenser of said gang, for

obtaining neutralization at short Wave lengths. I i l 6. In combination, a plurality of tunable oscillation circuits, an electron discharge tube coupling said circuits, fa uni-control, variable gang condenser for simultaneously and similarly tuning said circuits to a desired frequency in a a predetermined freconnected for tuning the input circuits of quency range, means for effectively counteracting feed-back of energy between said circuits at the low frequency end of said range, and additional means, including capacitive reactance produced between portions of said gang condenser during a portion of the vaof like sign as said first reactive means,

operative during adjustment of said tuning meansfto the high frequency end ofsai range, for effectively counteracting feed back of energy between the circuits at said high frequency end.

WALTER vim B. ROBERTS. 

